How a modular rear axle system can benefit automakers

German component supplier ZF has announced a new development which can enthuse automakers. The ability to offer driveline and chassis technology from a single source has always been one of the company’s major strengths – especially in the e-mobility era.

ZF is now using a new modular rear axle concept to demonstrate how a modular system architecture translates into even greater customer benefits. This innovative solution enables a vehicle with a twist beam axle or link SLA rear axle to be converted easily to a steerable rear axle concept with just a few modifications to the body. This is based on a non-driven basic axle in which an electric axle drive or a conventional rear axle drive as well as the AKC rear axle steering can be integrated, depending on customer requirements. Thus, vehicle manufacturers can respond extremely flexibly to various market requirements with just one body variant.

“With the new rear axle system, we are offering our customers wide-ranging applications in disparate vehicle segments. The solution can be used in hybrid, fuel-cell, and battery-powered vehicles and can be combined with conventional all-wheel modules or with our active rear axle steering AKC,” explains Uwe Coßmann, Head of the ZF Car Chassis Technology division. Development costs are also reduced considerably for automotive manufacturers: ZF handles the individual coordination of the internal interfaces in the axle construction kit.

The basic axle entails a modular further development of a Semi-Trailing Arm Rear Suspension (mSTARS). As part of this setup, the rear of the two outboard kinematics points of the lower control arm were replaced with an integral link and a toe link added. The toe link defines the track across the wheel hub and enables the toe-in to be adjusted precisely. As an alternative to a suspension strut, which tends to be used on semi-trailing link axles, the integral link in an extreme outboard position enables separate springs and dampers to be used. This solution tends to be cheaper and also provides more width between the wheel arches in the trunk.

Integrated electric axle drive system
The basic axle can be combined, for instance, with the electric drive module positioned centrally on the axle; this module features an electric motor configured as a high-revving asynchronous motor. The electric motor, the single-speed transmission with differential, housing, and cooling unit, as well as the power electronics complete with control software form an integrated, extremely compact unit.

Steering impulses from the rear
The basic axle can also be combined with ZF's AKC (Active Kinematics Control) rear axle steering. In this case, the rear wheels actively assist the front steering angle and the passenger car enjoys enhanced agility or stability, depending on the road speed, when changing direction.